206 
FXUS62 KGSP 231409
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1009 AM EDT Fri Apr 23 2021

.SYNOPSIS...
High pressure will bring dry weather again today. On Saturday a
low pressure system will bring shower and thunderstorm chances
to our area, and strong to severe storms are possible along and
south of Interstate 85. A cold front will pass through the area
by Sunday morning, followed by a return of dry and increasingly
warm weather through Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Friday...Mid and high clouds are a bit slow to spread
across the area within westerly flow aloft, and this is resulting in
temps warming up a bit quicker than current forecast. Still expect
increasing clouds across the area from late morning thru the aftn,
but generally with breaks and thin spots. So made minor tweaks
to the max temps to bump up a deg or two in spots. Otherwise,
no major changes with the morning update.

Otherwise, sfc high pressure will steadily drift eastward today
and move off the SE Coast later tonight, as the axis of a flattened
upper ridge moves overhead. This should allow for some modification
of the airmass and a gradual increase in moisture advection during
the later half of the period as winds pick up from the S to SW by
the afternoon. RH values will likely recover at least a small amount
compared to Thursday, yet they are still fcst to bottom-out in the
upper 20s to lower 30s. Thus, a Fire Danger Statement is in effect
for the entire CWA from noon until 6 PM. PoPs steadily ramp up from
west to east as the period ends early Saturday and deeper moisture
surges into the CWA and upglide increases. No measurable QPF is
expected until just after 06z on Saturday with the bulk of the QPF
expected after the near-term period ends. High temperatures will
rebound a fair amount compared to Thursday, but remain below normal.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 300 AM EDT Friday: At daybreak Saturday, a potent 500mb
trough axis is sitting over the Ozarks, with a more-or-less 
meridionally-oriented 250mb jet streak stacked over the 
Appalachians.  The trough spits lobes of DPVA into the Deep South.
The best forcing based on successive model runs looks to be centered
over northern MS/AL/GA, with somewhat less pronounced effects over
TN and the Carolinas.  In any case, steep height falls will promote
large-scale uplift over the course of Saturday, as a developing
surface low crosses the CWA from west to east and drags a trailing
cold front along with it.  Overall, this setup is beginning to
take on the appearance of a classical high-shear low-CAPE event.

So, as low-level mean flow backs to southwesterly Saturday
morning on the heels of departing high pressure to the east, we
should see rapid moisture advection from the Gulf of Mexico by
and after daybreak Saturday as what is essentially a warm front
pushes northward.  Meanwhile, isobars are beginning to take on the
classic cold wedge signature indicative of an in-situ CAD event.
So, it's safe to say we should be seeing at least light precip all
morning Saturday, from 12Z onward.  For now, models are trending
toward SBCAPE < 400 J/kg across the CWA, with the morning cloud
cover and light rainfall largely putting the damper on more robust
destabilization.  But, with an 850mb LLJ in place east of the
approaching cold front Saturday afternoon, 0-3km shear values
approach 50+ kts and put us squarely in the QLCS convective
mode assuming that the wedge indeed restricts CAPE values.

The worst impacts will likely be south of our CWA, where we see
more significant updraft helicity swaths and higher instability,
but we can't rule out some severe storms in our forecast area, 
especially in the southern tier of the SC Upstate.  At this time, 
the primary impacts should amount to damaging winds, and perhaps 
some isolated hail up to 1 inch in diameter.  Tornado threat remains 
low for now - 0-1km shear falls short of the 40kt threshold for 
concern, although latest model guidance produces a weak mesolow 
skirting the wedge boundary, which could act to enhance the low-
level shear.  In any case, we'll likely be right on the transition 
zone between severe impacts and relatively benign conditions. 
Nonetheless, even without any severe impacts we can anticipate storm 
total rainfall in the vicinity of 1 to 1.5 inches. Luckily, the last 
several days of dry weather should minimize hydro/flooding risk 
despite high QPFs. Saturday's high should be well below normal 
except perhaps in the far southern portions of the CWA, which may 
fall outside the cold wedge.

PoPs drop off significantly Saturday evening, with 00Z Sunday
marking the swift decline of convective chances.  Anticipating the
full cold frontal passage and shift to northwest flow by 06Z Sunday.
Temps will drop just enough that it's not out of the question
that we could see some isolated snow flurries at the very highest
mountain elevations before daybreak Sunday.  All that to say,
with the NAM bringing in much drier mid-level air, and models
still on track for gusty winds into the night, the odds seem
to be diminishing.  In any case, dry air rapidly filters in on
Sunday as high pressure builds in beneath broad 500mb ridging.
Saturday night's low, and Sunday's afternoon high temp should both
be near-normal.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 AM Fri: Upper level pattern will amplify Monday, with
a deep ridge taking shape over the Eastern Seaboard by Monday
night. This will allow dry sfc high pressure to migrate across
the coastal Southeast, and development of southerly return flow
Tuesday. Per 00z cycles of ECMWF, CMC-GDPS, and GEFS consensus,
it appears dry weather will persist thru Thursday with the slow
progression of the amplified pattern, with the southerly flow
only deepening. Thicknesses appear to peak Wednesday, and temps
will trend upward until then, with maxes reaching 7-10 degrees
above climo. Dewpoints will be seasonable, dare I say pleasant in
light of the sfc temps. The operational 00z GFS remains an early
outlier in bringing the trough and the attendant frontal system
east; it would suggest PoPs begin to ramp up Wednesday on the
southern-facing slopes, culminating in fropa Thursday. Going with
the slower consensus of the other guidance, the fropa is expected
after the end of the fcst period.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: Expect VFR conditions to continue thru the 
12z taf period at all taf sites except KCLT, where cig and visby 
restrictions will likely begin during the last 6 hours or so of the 
period as precip spreads over the area. Otherwise, broad surface 
high pressure will steadily track eastward thru the period and move 
off the SE Coast later tonight. Deeper moisture will begin to move 
into the fcst area from the west towards the end of the taf period 
early Sat and bring increasing VFR-lvl clouds. Expect winds to 
remain light and vrb to calm at most sites thru the overnight and 
into the morning and then pick back up from the S to SW by the 
afternoon. Speeds should remain in the 5 to 10 kt range with little 
in the way of gust potential.   

Outlook: A moist low pressure system will approach the fcst area 
early Sat with flight restrictions likely beginning Sat morning and 
persisting through the day with scattered to numerous showers and 
thunderstorms. Dry high pressure returns on Sunday and lingers thru 
the middle of next week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z 
KCLT       High 100%     High 100%     High 100%     High 100%     
KGSP       High 100%     High 100%     High 100%     High 100%     
KAVL       High 100%     High 100%     High 100%     High 100%     
KHKY       High 100%     High 100%     High 100%     High 100%     
KGMU       High 100%     High 100%     High 100%     High  93%     
KAND       High 100%     High 100%     High 100%     High  90%     

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation

&&

.FIRE WEATHER...
Winds will be much lower today compared to yesterday, but RH will be 
near critical levels. Will have another Fire Danger Statement for 
all counties.

Wetting rain still is not expected until this weekend across
the region.

&&

.CLIMATE...
RECORDS FOR 04-23

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      88 1960     42 1903     61 1957     29 1986    
   KCLT      91 1980     51 1901     64 1920     35 1986    
                1963                                        
                1960                                        
   KGSP      91 1980     48 1901     66 1920     32 1982    
                1963                                        
                1960

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Fire Danger Statement until 7 PM EDT this evening for GAZ010-
     017-018-026-028-029.
NC...Fire Danger Statement until 7 PM EDT this evening for NCZ033-
     035>037-048>053-056>059-062>065-068>072-082-501>510.
SC...Fire Danger Statement until 7 PM EDT this evening for 
     SCZ001>014-019.

&&

$$
SYNOPSIS...Wimberley
NEAR TERM...ARK/JPT
SHORT TERM...MPR
LONG TERM...Wimberley
AVIATION...JPT
FIRE WEATHER...
CLIMATE...